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Sceptical Hypotheses and Transcendental Arguments

Jonathan Barfield presents a way to beat the sceptics.

What if the world doesn’t really exist? Perhaps what I think is the real world is actually an illusion, or a computer simulation? Maybe I am really a brain in a vat of liquid goo, connected up by an evil scientist to electrodes producing nerve impulses that pump a simulation of a real world directly into my brain (cf. The Matrix)? Or what if nothing exists outside my mind? Perhaps the only thing that exists is my mind? Is anything I think about the world actually true?

Such deep questions and worries about what we can know about the world are called sceptical hypotheses. A sceptical hypothesis challenges our everyday assumptions about what is real and how we can know it, pushing us to accept the possibility that we might not know anything, or at least that we don’t have very much justification for some of the things that we usually assume we know.

One way of trying to overcome a sceptical hypothesis is to construct a theory of knowledge which sets out the criteria that have to be met in order for me to know something. I can then test any given claim to see if meets the standards I have set myself. The aim in constructing this theory is that we will then be able to demonstrate that we can in fact know that the world exists – that it isn’t an illusion or computer simulation – and that any other radically sceptical hypothesis is also false.

This strategy can be tricky: if you make your theory of knowledge too strict, then no claim will meet your criteria, in which case it will show you that you know nothing; if you make your theory of knowledge too slack, then it will indicate that you know some things that you otherwise don’t think you know. Plus, this approach encourages lengthy debate about exactly what the criteria for knowledge should be, how we should apply the criteria, and how we could be certain that the criteria have been met.

A different way to overcome a sceptical hypothesis is to use a transcendental argument. Transcendental arguments try to show that there is no way that the sceptical hypothesis could be true. That is, they try to show that a sceptical hypothesis can only be one of two things: it is either false, or it doesn’t make any sense in the first place. In either case, the hypothesis cannot be true. And if the sceptical hypothesis cannot be true, then we no longer need to worry about it! A transcendental argument does not beat the sceptical hypothesis directly by accepting the challenge to try and disprove it by providing a theory in response to it. Rather, a transcendental argument overcomes the sceptical hypothesis indirectly, by undermining its basis. It does this by showing that the hypothesis cannot be formulated without relying on the hypothesis being false.

Let’s look at two transcendental arguments which try to overcome sceptical hypotheses: Hilary Putnam trying to overcome the hypothesis that the external world might be a computer simulation; and Saul Kripke trying to overcome the hypothesis that perhaps nothing exists outside my mind.

Putnam’s Brain In A Vat

Perhaps what I think is the world is actually a computer simulation or other illusion? Maybe I am really a brain in a vat of goo connected up to electrodes that pump a simulation of a real world directly into my brain?

In Reason, Truth and History (1981), Hilary Putnam offers a transcendental argument to overcome the sceptical hypothesis that I might be a brain in a vat, or more generally, that what I think is the external world is actually some sort of simulation. Putnam’s transcendental argument is based on a theory about how our words work.

First, let’s suppose I am not a brain in a vat. In this situation, my words refer to real objects, and this reference to real objects is part of what those words mean. For example, my word ‘vat’ (usually) refers to real vats external to me, and this referring to real vats is part of what the word ‘vat’ means. So if I am not a brain in a vat, I can meaningfully say or think the hypothesis ‘I might be a brain in a vat’; but of course, in this situation we have stipulated that I am not a brain in a vat, so the hypothesis is false.

Now let’s suppose instead that I am a brain in a vat. In this situation, my words don’t mean what I think they mean: they don’t refer to the objects that I think they refer to, and my language doesn’t work the way I think it does, so I am consistently wrong about what I think my words mean. For example, in this situation – in the brain-in-a-vat setup – my word ‘vat’ can’t refer to any real vat external to me because I have never encountered any such object, only simulations or illusions of vats. Indeed, in this situation, my experiences of what I take to be vats are not of vats at all, but rather the result of calculated electrical stimulations sent directly into my brain. In this situation, my word ‘vat’ must then refer to some set of the electrical stimulation impulses sent into my brain. In fact, all of my words would be referring to such electrical impulses, and would never refer to real objects external to me, such as vats, because that wouldn’t be how my words could refer. So according to Putnam, in a situation where I was a brain in a vat, I could not truly or meaningfully say or think ‘I am a brain in a vat’, because my words only refer to electrical impulses, and not to real brains or real vats.

So in the first alternative, I am not a brain in a vat, but I can meaningfully, and falsely, say I am one. In the second alternative, I cannot meaningfully say or think that I am a brain in a vat because I cannot refer to real brains or vats, because my language doesn’t work in the way necessary for it to be meaningful. So, either I am not a brain in a vat, or I cannot coherently say or think that I am a brain in a vat; so either the sceptical hypothesis is false or the sceptical hypothesis doesn’t make any sense. Either way, the sceptical hypothesis that I might be a brain in a vat isn’t true. Putnam has therefore shown that the sceptical hypothesis cannot be asserted without relying on the hypothesis being false, as the sceptical hypothesis must be false in order for it to make sense. The general form of Putnam’s argument is that in order for our words, and therefore the sceptical hypothesis itself, to make sense, the sceptical hypothesis cannot be true: we cannot question whether the external world is real without assuming that the external world is real. If it makes sense for me to wonder whether I am a brain in a vat, then I am not one.

Kripke’s Language Checking

In Wittgenstein on Rules and Private Language (1982), Saul Kripke constructs a transcendental argument inspired by the later Ludwig Wittgenstein to overcome the sceptical hypothesis that there might be nothing that exists outside my mind, and that the only thing that really exists is my mind.

Kripke poses the Wittgensteinian question: How can I be sure that I am using my language consistently? For example, how can I be sure that I am using a word, such as ‘table’, the same way today as I was last week, and so be sure that my language use has a consistent meaning? Kripke then uses the Wittgensteinian argument that one of the main ways we can be sure of consistency in our language use is that other speakers of the language correct us if we use words incorrectly or inconsistently. In effect, the people I communicate with provide a checking service to make sure that I am using my words in the same way now as in the past, by ensuring that I am using words in the standard and consistent communal or public manner.

You might object that a far more useful way of checking that I am using my words in the same way now as in the past is to use my memory. However, as the Kripkean/Wittgensteinian argument goes, if I use my memory to check my word use, I also need a way of checking the reliability of my memory; and I can hardly check the reliability of my memory by using my memory. I will need another method. For example, if I want to catch a train, I might bring to mind a mental image of the train timetable and look at this image in my mind to find out what time the train will arrive. My memory of the train timetable might be reliable or it might not be: but the only way I can check the reliability of that memory is not to consult another memory, which may be equally fallible, but to check with a real physical train timetable. Or let’s suppose I wanted to keep a record of how frequently I experience a particular emotion – for example, a really specific feeling of loving affection. I resolve to write the letter ‘S’ in my diary whenever I experience this particular loving feeling. Having now done this for a few weeks, how can I be sure that each ‘S’ that I recorded refers to the same particular emotion? How can I be sure that some of the feelings weren’t significantly different? The only way I can check that each emotional experience was the same is to use my memory – but how am I to be sure that my memory is accurate and that I have indeed recorded ‘S’ consistently? I need a method of checking that my memory is reliable, but there does not seem to be a way of checking that my memory of using ‘S’ is reliable like I had in the train timetable example, so if I am only relying on my memory I have no way of checking I am using ‘S’ consistently.

Although I may use my memory to remember how I use words, the only way I can check that my memory is reliable (and hence that I am using my words in the same way now as in the past) is by consulting something outside my memory, such as other speakers of the language. Ultimately, I need some method of checking that I am using my words consistently that doesn’t rely solely on my memory.

How does this discussion about ensuring that I am using my language consistently help to overcome the sceptical hypothesis that there might be nothing that exists outside my mind, and that the only thing that really exists is my mind?

Well, either there is a world outside my mind including other language-speakers, or I have no means of ensuring that I am using my language consistently. However, in the latter case, I don’t know for sure the meaning of my own words – which, among other things, means that I cannot coherently talk or think about whether there is no world outside my mind. So either the sceptical hypothesis that there might not be a world outside my mind is false, or the sceptical hypothesis doesn’t make any sense, due to my not having a way of being sure that I know the meaning of my words. Either way, the sceptical hypothesis that there is nothing outside my mind isn’t true, which is what we were trying to prove. Thus Kripke also shows that this sceptical hypothesis cannot be made without relying on the hypothesis being false: I cannot question whether there is a world outside my mind without assuming that there is a world outside my mind, in order for my words, and therefore the sceptical hypothesis itself, to make sense. The sceptical hypothesis must be false in order for it to make sense. Or, if it makes sense for me to wonder whether there might not be a world outside my mind, then there is.

Kripke’s solution might perhaps inspire a further sceptical hypothesis: maybe there really is no way of checking that I am using my words consistently, and so I don’t know for certain the meaning of my own words; and so maybe I really am just talking nonsense. But we can construct a further transcendental argument to overcome this objection. I cannot meaningfully question whether I am talking nonsense without assuming that I am talking sense; so the further sceptical objection that I am talking nonsense must be false in order for it to make sense. Or, if it makes sense for me to wonder whether I am talking sense or not, then I am.

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